# Bright and dark fringes between two slits - waves

• Libra_girl
In summary, the two slits act as coherent sources of light, and at different points on the screen, the path difference between the two waves falling on that point varies, thus somewhere they interfere constructively (bright point, maxima) and at some points they interfere destructively (minima, dark band). This causes a bright fringe to be formed where the path difference is an integral multiple of lambda, and a dark band is formed when the path difference is not an integral multiple of lambda.
Libra_girl

## Homework Statement

Explain why we observe bright and dark fringes behind two thin slits illuminated by monochromatic light?

## Homework Equations

Explain and justify the mathematical condition that determines whether a dark or bright fringe is formed.

## The Attempt at a Solution

Google for youngs double slit experiment :)

Yep, owls is absolutely right. Here is an interesting link I found
( I don't have 15 posts yet thus I can't copy paste the link )
google for "young's double slit experiment" and click on the second link

If you still need help on this one, let us know

The two slits act as coherent sources of light, and at different points on the screen, the path difference between the two waves falling on that point varies, thus somewhere they interfere constructively (bright point, maxima) and at some points they interfere destructively (minima, dark band).

lambda / d = x/ L
d is distance between slits, lambda is the wavelength of monochromatic light, x is distance of first bright fringe from central maxima, L is distance of screen from the slits.
a bright fringe is obtained where the path difference between the light from the two slits is an integral multiple of lambda. so where
path diff = n.lamda .. bright fringe is obtained.
and when path difference is (2n-1).lambda/2 ...a dark band is obtained.

armis said:
Yep, owls is absolutely right. Here is an interesting link I found
( I don't have 15 posts yet thus I can't copy paste the link )
google for "young's double slit experiment" and click on the second link

If you still need help on this one, let us know

spideyunlimit said:
The two slits act as coherent sources of light, and at different points on the screen, the path difference between the two waves falling on that point varies, thus somewhere they interfere constructively (bright point, maxima) and at some points they interfere destructively (minima, dark band).

lambda / d = x/ L
d is distance between slits, lambda is the wavelength of monochromatic light, x is distance of first bright fringe from central maxima, L is distance of screen from the slits.
a bright fringe is obtained where the path difference between the light from the two slits is an integral multiple of lambda. so where
path diff = n.lamda .. bright fringe is obtained.
and when path difference is (2n-1).lambda/2 ...a dark band is obtained.

owls said:
Google for youngs double slit experiment :)

Thank you all.

## What is the phenomenon of bright and dark fringes between two slits?

The phenomenon of bright and dark fringes between two slits is known as the interference of waves. It occurs when a wave passes through two narrow slits and creates a pattern of alternating bright and dark regions on a screen placed behind the slits.

## What causes the formation of bright and dark fringes between two slits?

The formation of bright and dark fringes is caused by the constructive and destructive interference of waves. When two waves with the same frequency and amplitude meet, they can either add up to create a brighter region (constructive interference) or cancel each other out to create a darker region (destructive interference).

## How does the distance between the two slits affect the pattern of bright and dark fringes?

The distance between the two slits, also known as the slit separation, directly affects the spacing of the fringes. As the distance increases, the fringes become wider and more spread out. This is because a larger slit separation allows for more interference patterns to form.

## What type of waves can produce bright and dark fringes between two slits?

Any type of wave can produce this phenomenon, as long as it meets certain conditions. This includes light waves, sound waves, and water waves. However, the wavelength of the waves must be smaller than the slit separation in order for the interference patterns to be visible.

## How can the pattern of bright and dark fringes be used in scientific experiments?

The pattern of bright and dark fringes can be used to measure the wavelength of a wave. By observing the distance between fringes and knowing the slit separation, scientists can calculate the wavelength of the wave passing through the slits. This can also be used to study the properties of different types of waves and to test the principles of wave interference.

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